Secondary Battery

ABSTRACT

The secondary battery includes an electrode assembly to which an electrode lead is attached; a case configured to receive the electrode assembly therein; a lead film configured to surround a part of an outer surface of the electrode lead and interposed between the electrode lead and the case; a vent region formed in at least a part of the case; and a vent member inserted into the vent region and configured to contain linear low-density polyethylene having a poly dispersity index (PDI) of 4 or less, wherein the vent member has a maximum sealing strength of less than 6 kgf/15 mm at 100° C. or above and a maximum sealing strength of 6 kgf/15 mm or more at room temperature to 60° C.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to Korean Patent Application No.10-2021-0049378 filed on Apr. 15, 2021 and Korean Patent Application No.10-2021-0150951 filed on Nov. 4, 2021, the disclosures of which areincorporated herein by reference in their entirety.

TECHNICAL FIELD

The present disclosure relates to a secondary battery, and moreparticularly, to a secondary battery having a vent member.

BACKGROUND

Secondary batteries are highly applicable to various products andexhibit superior electrical properties such as high energy density, etc.Secondary batteries are commonly used not only in portable devices butalso in electric vehicles (EVs) or hybrid electric vehicles (HEVs)driven by electrical power sources. The secondary battery is drawingattentions as a new energy source for enhancing environment friendlinessand energy efficiency in that the use of fossil fuels can be reducedgreatly and no byproduct is generated during energy consumption.

Secondary batteries widely used at present include lithium ionbatteries, lithium polymer batteries, nickel cadmium batteries, nickelhydrogen batteries, nickel zinc batteries and the like.

The secondary battery generally has a structure in which an electrodeassembly including at least one unit cell having a positiveelectrode/separator/negative electrode structure is accommodated in acase of a laminate sheet in which an outer layer, a metal barrier layerand a sealant layer are sequentially laminated, and a sealant resin ofthe sealant layer is fused to seal the electrode assembly is sealed.

In the conventional secondary battery, the battery may ignite due tovarious causes such as a short circuit inside the secondary battery,overcharge or overdischarge, temperature control, or the like. At thistime, thermal propagation where the temperature inside the secondarybattery rises rapidly and simultaneously the heat is transferred toneighboring cells may be generated, which may further increase the fire.

In order to minimize damage to the electrode caused by gas when thermalpropagation occurs—i.e., when the internal temperature of the secondarybattery rises, the directional venting characteristic is required todischarge the gas in one direction. However, the conventional secondarybattery has a problem in that it is difficult to induce gas discharge ina specific direction.

Therefore, the present disclosure is directed to providing a secondarybattery with improved safety by inducing gas discharge in a specificdirection.

BRIEF SUMMARY OF THE INVENTION

Disclosed herein are secondary batteries with a vent member.

In accordance with an aspect of the present disclosure, there isprovided a secondary battery. The secondary battery may include anelectrode assembly to which an electrode lead is attached; a caseconfigured to receive the electrode assembly therein; a lead filmconfigured to surround a part of an outer surface of the electrode leadand interposed between the electrode lead and the case; a vent regionformed in at least a part of the case; and a vent member inserted intothe vent region and configured to contain linear low-densitypolyethylene having a poly dispersity index (PDI) of 4 or less. The ventmember has a maximum sealing strength of less than 6 kgf/15 mm at 100°C. or above and a maximum sealing strength of 6 kgf/15 mm or more atroom temperature to 60° C.

Continuing in accordance with this aspect, the vent member may have anaverage sealing strength of less than 4.5 kgf/15 mm at 100° C. or above.

Continuing in accordance with this aspect, the vent member may have anaverage sealing strength of 4.5 kgf/15 mm or more at room temperature to60° C.

Continuing in accordance with this aspect, the case may include asealing portion formed to seal the electrode assembly. The sealingportion may contain a sealant resin. The vent member containing thelinear low-density polyethylene having a comonomer with a carbon numberof 6 or more may have a lower melting point than the sealant resin.

Continuing in accordance with this aspect, the vent member may melt at100° C. to 120° C. to vent gases.

Continuing in accordance with this aspect, the vent member may be ventedat a pressure of 1.5 atm or more.

Continuing in accordance with this aspect, the linear low-densitypolyethylene may be polymerized in the presence of a metallocenecatalyst.

Continuing in accordance with this aspect, a difference between acrystallization temperature of the sealant resin and a crystallizationtemperature of the linear low-density polyethylene may be 10° C. orless.

Continuing in accordance with this aspect, the linear low-densitypolyethylene may have a crystallization temperature of 90° C. to 115° C.

Continuing in accordance with this aspect, the linear low-densitypolyethylene may have a melting point of 100° C. to 130° C.

Continuing in accordance with this aspect, the linear low-densitypolyethylene may have a weight-average molecular weight of 100,000 g/molto 400,000 g/mol.

Continuing in accordance with this aspect, the vent region may belocated in the sealing portion.

Continuing in accordance with this aspect, the vent region may belocated in a sealing portion at a corner of the case.

Continuing in accordance with this aspect, the secondary battery may bea pouch-type secondary battery.

Continuing in accordance with this aspect, the vent member may have amaximum sealing strength of less than 6 kgf/15 mm at 100° C. to 120° C.

Continuing in accordance with this aspect, the vent member may have anaverage sealing strength of less than 4.5 kgf/15 mm at 100° C. to 120°C.

Continuing in accordance with this aspect, the linear low-densitypolyethylene may have a poly dispersity index (PDI) of from 1 to 4.

Continuing in accordance with this aspect, the vent member may have amaximum sealing strength of less than 3 kgf/15 mm at 120° C. or more.

Continuing in accordance with this aspect, the vent member may have anaverage sealing strength of less than 2 kgf/15 mm at 120° C. or more.

A secondary battery according to an embodiment of the present disclosuremay include the vent member has a maximum sealing strength of less than6 kgf/15 mm at 100° C. or above and a maximum sealing strength of 6kgf/15 mm or more at room temperature to 60° C. Accordingly, it ispossible to secure the sealing property of the battery at roomtemperature to 60° C. and induce gas discharge toward the vent region at100° C. or above. Accordingly, the safety of the battery is improved.

A secondary battery according to an embodiment of the present disclosuremay include a vent member containing linear low-density polyethylenehaving a poly dispersity index (PDI) of 4 or less. Accordingly, it ispossible to secure the sealing property of the battery at the normaloperation temperature of the battery.

DESCRIPTION OF DRAWINGS

The accompanying drawings illustrate a preferred embodiment of thepresent disclosure and together with the foregoing disclosure, serve toprovide further understanding of the technical features of the presentdisclosure, and thus, the present disclosure is not construed as beinglimited to the drawing.

FIG. 1 is an exploded perspective view showing a secondary batteryaccording to an embodiment of the present disclosure.

FIG. 2 is a plan view showing the secondary battery according to anembodiment of the present disclosure.

FIG. 3 is a diagram showing a state in which a vent occurs in thesecondary battery according to an embodiment of the present disclosure.

FIG. 4 is a plan view showing a secondary battery according to anotherembodiment of the present disclosure.

FIG. 5 is a plan view showing a secondary battery according to anotherembodiment of the present disclosure.

FIG. 6 is a plan view showing a secondary battery according to anotherembodiment of the present disclosure.

FIG. 7 is a plan view showing a secondary battery according to anotherembodiment of the present disclosure.

DETAILED DESCRIPTION

Hereinafter, preferred embodiments of the present disclosure will bedescribed in detail with reference to the accompanying drawings. Priorto the description, it should be understood that the terms used in thespecification and the appended claims should not be construed as limitedto general and dictionary meanings, but interpreted based on themeanings and concepts corresponding to technical aspects of the presentdisclosure on the basis of the principle that the inventor is allowed todefine terms appropriately for the best explanation.

Therefore, the description proposed herein is just a preferable examplefor the purpose of illustrations only, not intended to limit the scopeof the disclosure, so it should be understood that other equivalents andmodifications could be made thereto without departing from the scope ofthe disclosure.

In general, the battery operates normally below 100° C., especially atroom temperature to 60° C. or below. However, if an abnormal reactionoccurs, the temperature of the battery may rise. If the temperature ofthe battery rises, problems such as gas generation inside the batteryoccur. In particular, if the temperature of the battery becomes 100° C.or higher, the battery swells more seriously due to the gas generatedinside the battery.

The inventors have completed the invention by designing a batterycapable of securing the sealing property of the battery at the normaloperation temperature of the battery and inducing a vent at a hightemperature.

A secondary battery according to one aspect of the present disclosureincludes an electrode assembly to which an electrode lead is attached; acase configured to accommodate the electrode assembly; a lead filmconfigured to surround a part of an outer surface of the electrode leadand interposed between the electrode lead and the case; a vent regionformed in at least a part of the case; and a vent member inserted intothe vent region and configured to contain linear low-densitypolyethylene having a poly dispersity index (PDI) of 4 or less, whereinthe vent member has a maximum sealing strength of less than 6 kgf/15 mmat 100° C. or above and a maximum sealing strength of 6 kgf/15 mm ormore at room temperature to 60° C.

FIGS. 1 and 2 show a secondary battery according to an embodiment of thepresent disclosure.

A secondary battery 10 includes an electrode assembly 12 to which anelectrode lead 11 is attached, and a case 13.

The electrode assembly 12 includes a positive electrode plate, anegative electrode plate and a separator. In the electrode assembly 12,a positive electrode plate and a negative electrode plate may besequentially laminated with a separator being interposed therebetween.

The positive electrode plate may include a positive electrode currentcollector made of a metal thin film having excellent conductivity, forexample an aluminum (Al) foil, and a positive electrode active materiallayer coated on at least one surface thereof. In addition, the positiveelectrode plate may include a positive electrode tab made of a metalmaterial—for example, an aluminum (Al) material, at one side endthereof. The positive electrode tab may protrude from one side end ofthe positive electrode plate. The positive electrode tab may be weldedto one side end of the positive electrode plate, or be bonded theretousing a conductive adhesive.

The negative electrode plate may include a negative electrode currentcollector made of a conductive metal thin film—for example, a copper(Cu) foil, and a negative electrode active material layer coated on atleast one surface thereof. In addition, the negative electrode plate mayinclude a negative electrode tab formed of a metal material, for examplea nickel (Ni) material, at one side end thereof. The negative electrodetab may protrude from one side end of the negative electrode plate. Thenegative electrode tab may be welded to one side end of the negativeelectrode plate, or be bonded thereto using a conductive adhesive.

The separator is located between the positive electrode plate and thenegative electrode plate to electrically insulate the positive electrodeplate and the negative electrode plate from each other. The separatormay be a porous membrane so that lithium ions can pass between thepositive electrode plate and the negative electrode plate. The separatormay include, for example, a porous membrane using polyethylene (PE), orpolypropylene (PP), or a composite film thereof.

An inorganic coating layer may be provided on the surface of theseparator. The inorganic coating layer may have a structure in whichinorganic particles are bonded to each other by a binder to form aninterstitial volume between the particles.

The electrode assembly 12 may be a jelly-roll (winding-type) electrodeassembly having a structure in which long sheet-type positive andnegative electrodes are wound with a separator being interposedtherebetween, a stacked (stack-type) electrode assembly having astructure in which a plurality of positive and negative electrodes cutinto units of a predetermined size are sequentially stacked with aseparator being interposed therebetween, a stack/folding type electrodeassembly having a structure in which bi-cells or full-cells wherepositive and negative electrodes of a predetermined unit are stackedwith a separator being interposed therebetween are wound, or the like.

The case 13 serves to accommodate the electrode assembly 12.

In an embodiment of the present disclosure, the case 13 may include anaccommodation portion 13 a for accommodating the electrode assembly 12,and a sealing portion 13 b formed to seal the electrode assembly 12 asshown in FIG. 1.

The sealing portion 13 b may include a sealant resin, and the sealantresin may be fused along the outer circumference of the accommodationportion 13 a to seal the electrode assembly 12.

In an embodiment of the present disclosure, the case 13 may be providedin a film form having a multilayer structure including an outer layerfor protection against external impacts, a metal barrier layer forblocking moisture, and a sealant layer for sealing the case.

The outer layer may include a polyester-based film using poly(ethyleneterephthalate) (PET), polybutylene terephthalate, polyethylenenaphthalate, polybutylene naphthalate, co-polyester, polycarbonate,nylon, or the like, and may be configured in a single layer or multiplelayers.

The metal barrier layer may include aluminum, copper, or the like.

The sealant layer may contain a sealant resin and may be configured in asingle layer or multiple layers.

The sealant resin may include polypropylene (PP), acid-modifiedpolypropylene (PPa), random polypropylene, ethylene propylene copolymer,or two or more thereof. The ethylene propylene copolymer may include,but is not limited to, ethylene-propylene rubber, ethylene-propyleneblock copolymer, and the like.

In an embodiment of the present disclosure, the case 13 may be in apouch form.

The pouch-type battery case 13 may include an upper pouch and a lowerpouch. If the case 13 includes an upper pouch and a lower pouch, afterthe upper pouch and the lower pouch are positioned so that the sealantresins thereof face each other, the facing sealant resins may be fusedto each other by heat and pressure to have a structure that seals thebattery.

The fusion of the sealing portion 13 b may be thermal fusion, ultrasonicfusion, or the like, but is not particularly limited as long as thesealing portion 13 b can be fused.

The sealing portion 13 b may be sealed on four or three peripheral sidesthe case 13 in some embodiments. In the three-sided sealing structure,after the upper pouch and the lower pouch are formed on one pouch sheet,the boundary surface between the upper pouch and the lower pouch is bentso that the electrode assembly accommodation portions 13 a formed on theupper pouch and the lower pouch overlap, and in this state, the edges ofthe remaining three sides are sealed except for the bending portion.

The electrode lead 11 may be accommodated in the case 13 so that a partthereof is exposed to the outside of the case 13 as shown in FIG. 1.

Secondary battery 10 according to an embodiment of the presentdisclosure includes a lead film 14. The lead film 14 surrounds a part ofthe outer surface of the electrode lead 11. and the lead film 14 isinterposed between the electrode lead 11 and the case 13. For example,the lead film 14 may be interposed between the electrode lead 11 and thesealing portion 13 b of the case 13 in a portion where the electrodelead 11 protrudes or extends away from case 13 to help the bonding ofthe electrode lead 11 and the case 13.

Referring to FIGS. 1 and 2, the secondary battery 10 according to anembodiment of the present disclosure has a vent region (not shown)formed in at least a part of the case 13, and a vent member 15 may beinserted into the vent region. When thermal propagation occurs, the ventmember 15 may induce the discharge of gas in a specific direction,thereby improving the safety of the battery.

The vent member 15 and the case 13 may overlap by means of thermalfusion. In another example, the vent member 15 and the case 13 may beoverlapped by means of an adhesive such as glue. In another example, thevent member 15 and the case 13 may be physically coupled to each otherby means of a clip or the like. In another example, at least a part ofthe vent member 15 may be embedded in a film constituting the case 13,for example a sealant resin.

The vent member 15 has a maximum sealing strength of less than 6 kgf/15mm at 100° C. or higher. If the vent member 15 satisfies theabove-mentioned sealing strength in the above-mentioned temperaturerange, the sealing strength of the part of the case 13 in which the ventmember 15 is inserted is lowered at 100° C. or higher, so that the ventcharacteristic may be readily implemented.

When the vent member 15 has a maximum sealing strength of 6 kgf/15 mm ormore at 100° C. or higher, the sealing strength of the part of the case13 in which the vent member 15 is inserted is too strong at 100° C. orhigher to induce a vent at a high temperature.

The vent member 15 has a maximum sealing strength of 6 kgf/15 mm or moreat room temperature to 60° C. If the vent member 15 satisfies theabove-mentioned sealing strength in the above temperature range, even ifthe vent member 15 is inserted, the part of the case 13 in which thevent member 15 is inserted has excellent sealing strength at roomtemperature to 60° C., which may easily secure the sealing property ofthe battery.

When the vent member 15 has a maximum sealing strength of less than 6kgf/15 mm at room temperature to 60° C., it is difficult to securesealing properties of the battery at room temperature to 60° C. in thepart of the case 13 into which the vent member 15 is inserted.

In an embodiment of the present disclosure, the vent member 15 may havea maximum sealing strength of less than 5 kgf/15 mm or less than 4.5kgf/15 mm at 100° C. or higher. In an embodiment of the presentdisclosure, the vent member 15 may have a maximum sealing strength ofless than 6 kgf/15 mm or less than 5 kgf/15 mm or less than 4.5 kgf/15mm at 100° C. to 120° C. In an embodiment of the present disclosure, thevent member 15 may have a maximum sealing strength of less than 3 kgf/15mm or less than 2 kgf/15 mm or less than 1 kgf/15 mm or less than 0.5kgf/15 mm at 120° C. or higher. If the vent member 15 satisfies theabove-mentioned sealing strength in the above-mentioned temperaturerange, the sealing strength of the part of the case 13 in which the ventmember 15 is inserted may be lowered at 100° C. or higher, so that thevent characteristic may be readily implemented.

In an embodiment of the present disclosure, the vent member 15 may havea maximum sealing strength of 8 kgf/15 mm or more or 10 kgf/15 mm ormore at room temperature to 60° C. If the vent member 15 satisfies theabove-mentioned sealing strength in the above temperature range, even ifthe vent member 15 is inserted, the part of the case 13 in which thevent member 15 is inserted may have excellent sealing strength at roomtemperature to 60° C., which may easily secure the sealing property ofthe battery.

In an embodiment of the present disclosure, the vent member 15 may havean average sealing strength of less than 4.5 kgf/15 mm or less than 3kgf/15 mm at 100° C. or above. In an embodiment of the presentdisclosure, the vent member 15 may have an average sealing strength ofless than 4.5 kgf/15 mm or less than 3 kgf/15 mm at 100° C. to 120° C.In an embodiment of the present disclosure, the vent member 15 may havean average sealing strength of less than 2 kgf/15 mm or less than 1kgf/15 mm or less than 0.5 kgf/15 mm at 120° C. or higher. If the ventmember 15 satisfies the above-mentioned sealing strength in theabove-mentioned temperature range, the sealing strength of the part ofthe case 13 in which the vent member 15 is inserted may be lowered at100° C. or above, so that the vent characteristic may be implementedmore easily.

In an embodiment of the present disclosure, the vent member 15 may havean average sealing strength of 4.5 kgf/15 mm or more or 5 kgf/15 mm ormore or 6 kgf/15 mm or more or 7 kgf/15 mm or more at room temperatureto 60° C. If the vent member 15 satisfies the above-mentioned sealingstrength in the above temperature range, even if the vent member 15 isinserted, the part of the case 13 in which the vent member 15 isinserted may have excellent sealing strength at room temperature to 60°C., thereby easily securing the sealing property.

In an embodiment of the present disclosure, the vent member 15 may havean average sealing strength of less than 4.5 kgf/15 mm at 100° C. orabove. The vent member 15 may have an average sealing strength of 4.5kgf/15 mm or more at room temperature to 60° C. If the vent member 15has the above-mentioned sealing strength in the above-describedtemperature range, the sealing strength of the part of the case 13 inwhich the vent member 15 is inserted may be lowered at 100° C. or above,so that the vent characteristic may be easily implemented. In addition,since the case 13 has excellent sealing strength at room temperature to60° C., the sealing property of the battery may be easily secured.

The sealing strength of the vent member 15 according to temperature maybe measured by conducting a tensile test at a speed of 5 mm/min, aftercutting the part of the case 13 in which the vent member 15 is insertedinto a width of 15 mm and a length of 5 cm and then biting both endsthereof using a UTM jig in a state where both ends are spread to 180°.

At this time, the maximum sealing strength means a maximum value whenthe case 13 is broken, and the average sealing strength means an averagevalue when the case 13 is stretched by 8 mm at 4.5 kgf/15 mm when themaximum sealing strength is 4.5 kgf/15 mm or more and an average valuewhen the case 13 is stretched by 8 mm at the maximum sealing strengthwhen the maximum sealing strength is less than 4.5 kgf/15 mm.

FIG. 3 is a diagram showing a state in which a vent occurs in thesecondary battery according to an embodiment of the present invention.Specifically, FIG. 3 is a cross-sectional view showing the vent memberin the secondary battery according to an embodiment of the presentinvention.

Referring to FIG. 3, at a temperature at which the battery normallyoperates, for example at room temperature to 60° C., the vent member hasan excellent sealing strength so that the vent region where the ventmember is inserted serves to seal the case from the outside. If thetemperature of the battery is excessively increased due to abnormaloperation of the battery, for example if the temperature of the batterybecomes 100° C. or above, as the sealing strength of the vent member islowered, the sealing strength of the portion into which the vent memberis inserted is reduced, so that the vent may be guided to this portion.For example, as the pressure of the gas inside the battery is applied tothe interface between the vent member and the case so that a gap isformed between the vent member and the case, the vent may be guidedthereto.

In an embodiment of the present disclosure, the vent member 15 may bevented at 100° C. to 120° C. to expel or exhaust gases from theaccommodation portion to outside the secondary battery. In particular,the vent member 15 may be vented at 100° C. to 120° C. with a pressureof 1.5 atm or more. As the vent member 15 is vented in theabove-described temperature range and/or the above-mentioned pressurecondition, it is easier to seal the battery during normal operation ofthe battery and to induce gas discharge only during abnormal operationof the battery.

The vent member contains linear low-density polyethylene having a polydispersity index (PDI) of 4 or less. If the poly dispersity index of thelinear low-density polyethylene satisfies the above range, the molecularweight distribution is narrow, so the sealing strength and propertiesmay be excellent during normal operation of the battery, for example atroom temperature to 60° C.

In an embodiment of the present disclosure, the linear low-densitypolyethylene may have a poly dispersity index (PDI) of 3.8 or less, or3.796 or less, or 3.5 or less, or 3.023 or less, or 3 or less, or 2.7 orless, or 2.674 or less. In addition, the poly dispersity index (PDI) maybe 1.0 or more. If the poly dispersity index of the linear low-densitypolyethylene satisfies the above range, the molecular weightdistribution is narrow, so the sealing strength and properties may bemore excellent during normal operation of the battery.

In an embodiment of the present disclosure, the linear low-densitypolyethylene may have a weight-average molecular weight of 100,000 g/molto 400,000 g/mol, or 200,000 g/mol to 350,000 g/mol, or 230,000 g/mol to300,000 g/mol. If the weight-average molecular weight of the linearlow-density polyethylene satisfies the above-described range, thesealing strength of the vent member may be improved during normaloperation of the battery. For example, this may allow the vent member tomore easily have a maximum sealing strength of 6 kgf/15 mm or more atroom temperature to 60° C.

The weight-average molecular weight and the poly dispersity index of thelinear low-density polyethylene may be measured by gel permeationchromatography (GPC) under the following conditions.

-   -   column: Tosoh, HLC-8321 GPC/HT    -   solvent: TCB (Trichlorobenzene)+0.04% BHT (after drying with        0.1% CaCl₂)    -   flow velocity: 1.0 ml/min    -   sample concentration: 1.5 mg/ml    -   dose: 300 μl    -   column temperature: 160° C.    -   Detector: RI detector    -   Standard: Polystyrene (calibrated with a third-order function)

In an embodiment of the present disclosure, the linear low-densitypolyethylene may have a lower melting point than the sealant resin. Ifthe linear low-density polyethylene has a lower melting point than thesealant resin, the vent member may be melted faster than the sealantresin at high temperature. Accordingly, the sealing strength of theportion where the vent member 15 is inserted may be further loweredcompared to the sealing strength of the case portion containing thesealant resin at high temperature, so that the venting characteristicmay be readily implemented.

In an embodiment of the present disclosure, the linear low-densitypolyethylene may have a melting point of 100° C. to 130° C., or 105° C.to 125° C., or 110° C. to 120° C. If the melting point of the linearlow-density polyethylene satisfies the above-mentioned range, thesealing strength of the case 13 in which the vent member 15 is insertedmay be lowered at a high temperature, for example 100° C. or higher, sothat the venting characteristic may be readily implemented. In addition,this may allow the vent member to more easily have a maximum sealingstrength of less than 6 kgf/15 mm at 100° C. or higher and a maximumsealing strength of 6 kgf/15 mm or more at room temperature to 60° C.

The melting point of the linear low-density polyethylene may be measuredusing a differential scanning calorimeter (DSC). For example, thetemperature of a sample is increased from 30° C. to 280° C. at 10°C./min, maintained at 280° C. for 10 minutes, cooled to 30° C. at 10°C./min, and then maintained at 30° C. for 10 minutes. Then, afterincreasing the temperature of the sample from 30° C. to 280° C. at 10°C./min, the melting point may be measured by maintaining the temperatureat 280° C. for 10 minutes.

In an embodiment of the present disclosure, the linear low-densitypolyethylene may be polymerized in the presence of a metallocenecatalyst. If the linear low-density polyethylene is polymerized in thepresence of a metallocene catalyst, it may be more advantageous in termsof sealing strength and properties, compared to the case where it ispolymerized in the presence of a Ziegler-Natta catalyst. For example,this may allow the vent member containing linear low-densitypolyethylene to more easily have a maximum sealing strength of less than6 kgf/15 mm at 100° C. or higher and a maximum sealing strength of 6kgf/15 mm or more at room temperature to 60° C.

In an embodiment of the present disclosure, the crystallizationtemperature of the sealant resin and the crystallization temperature ofthe linear low-density polyethylene may be similar. For example, thedifference between the crystallization temperature of the sealant resinand the crystallization temperature of the linear low-densitypolyethylene may be 10° C. or less, or 5° C. or less. In addition, thedifference between the crystallization temperature of the sealant resinand the crystallization temperature of the linear low-densitypolyethylene may be 0.1° C. or more. If the difference between thecrystallization temperature of the sealant resin and the crystallizationtemperature of the linear low-density polyethylene satisfies the aboverange, the sealant resin and the linear low-density polyethylene mayhave more excellent fusion characteristic during normal operation of thebattery. For example, this may allow the vent member containing linearlow-density polyethylene to more easily have a maximum sealing strengthof 6 kgf/15 mm or more at room temperature to 60° C.

In an embodiment of the present disclosure, the linear low-densitypolyethylene may have a crystallization temperature of 90° C. to 115°C., or 95° C. to 110° C., or 100° C. to 110° C., or 105° C. to 110° C.If the crystallization temperature of the linear low-densitypolyethylene satisfies the above range, the sealant resin and the linearlow-density polyethylene may have improved fusion characteristics.

In an embodiment of the present disclosure, the difference between thecrystallization temperature of the sealant resin and the crystallizationtemperature of the linear low-density polyethylene may be 10° C. orless, and the linear low-density polyethylene may have a crystallizationtemperature of 90° C. to 115° C.

The crystallization temperature may be measured using a differentialscanning calorimeter (DSC). For example, the temperature of the samplemay be increased from 30° C. to 280° C. at 10° C./min, maintained at280° C. for 10 minutes, cooled to 30° C. at 10° C./min, and thenmaintained at 30° C. for 10 minutes. Then, after increasing thetemperature of the sample from 30° C. to 280° C. at 10° C./min, thecrystallization temperature may be measured by maintaining thetemperature at 280° C. for 10 minutes.

In an embodiment of the present disclosure, the vent member 15 may havevarious shapes so that gas is easily directed toward the vent region.For example, the vent member 15 may have a film shape.

The vent member 15 may be formed to have a predetermined thickness of apreset size.

In an embodiment of the present disclosure, as shown in FIGS. 1 and 2,the vent member (15) may be located in a sealing portion.

Referring to FIG. 2, the vent member 15 may be located in the sealingportion at a corner side of the case. For example, the vent member 15may be located at a corner side of the sealing portion where theelectrode lead 11 is exposed to the outside. Specifically, the ventmember 15 may be located at the sealing portion beside the electrodeleads 11, except for a region between the electrode leads 11. If thevent member 15 is located at the corner side of the sealing portionwhere the electrode lead 11 is exposed to the outside, the amount of gasvented toward the electrode lead 11 may be minimized, thereby furtherenhancing the safety of the battery.

In an embodiment of the present disclosure, if the sealing portion 13 bis sealed on three sides, the bent side of the case and one end of thevent member 15 may be in close contact.

In addition, the vent member 15 may be inserted into the case 13 so thatits insertion length may be varied, or its venting pressure and positionmay be controlled depending on the design requirements. Here, theinsertion length of the vent member means a maximum value of thedistance between one end and the other end of the vent member based onthe protruding direction of the electrode lead.

For example, as shown in FIG. 4, the insertion length of the vent member15 may be smaller than the width of the sealing portion 13 b. Forexample, the insertion length of the vent member 15 may be less thanabout 50% of the width of the sealing portion 13 b. Here, the width ofthe sealing portion 13 b means a maximum value of the distance betweenone end and the other end of the sealing portion 13 b based on theprotruding direction of the electrode lead 11.

Alternatively, as shown in FIG. 5, the insertion length of the ventmember 15 may be greater than the width of the sealing portion 13 b. Forexample, the vent member 15 may be inserted to be exposed out of thecase 13 through the accommodation portion 13 a.

In an embodiment of the present disclosure, the vent member 15 mayfurther include an adhesive layer for improved placement.

FIG. 6 is a plan view showing a secondary battery according to anotherembodiment of the present disclosure.

Referring to FIG. 6, the vent member 15 may be located in the sealingportion excluding a sealing portion where the electrode lead 11 isexposed to the outside.

FIG. 7 is a plan view showing a secondary battery according to anotherembodiment of the present disclosure.

Referring to FIG. 7, the vent member 15 may be located in the sealingportion where the electrode lead 11 is exposed to the outside. Forexample, the vent member 15 may be located in the sealing portionbetween the electrode lead 11 and the electrode lead 11.

Since the secondary battery according to an embodiment of the presentdisclosure includes the vent member containing linear low-densitypolyethylene having a poly dispersity index (PDI) of 4 or less, and thevent member has a maximum sealing strength of less than 6 kgf/15 mm at100° C. or above and a maximum sealing strength of 6 kgf/15 mm or moreat room temperature to 60° C., directional venting for discharging gasin a specific direction by lowering the sealing strength at hightemperature may be implemented more conveniently and efficiently,thereby minimize damage to the electrode caused by gas when thermalpropagation occurs—i.e., when the internal temperature of the secondarybattery rise.

In an embodiment of the present disclosure, the secondary battery may bea cylindrical, prismatic, or pouch-type secondary battery. Among them,the secondary battery may be a pouch-type secondary battery.

Hereinafter, examples will be described in detail to help understandingof the present disclosure. However, embodiments according to the presentdisclosure may be modified in various other forms, and the scope of thepresent disclosure should not be construed as being limited to thefollowing examples. Examples of the present disclosure are provided tomore fully explain the present disclosure to a person with averageknowledge in the art.

Example 1

After the upper pouch and the lower pouch on which poly(ethyleneterephthalate))/aluminum foil/polypropylene resin are laminated in orderwere disposed so that the polypropylene resins face each other, anelectrode assembly in which positive electrode/separator/negativeelectrode were stacked in order was accommodated therein.

After that, the vent member containing linear low-density polyethylene(ExxonMobile, Exceed™, 1018) having a comonomer with a carbon number of6 polymerized in the presence of a metallocene catalyst was insertedbetween the polypropylene resins and then thermally fused, therebymanufacturing a secondary battery.

Example 2

A secondary battery was manufactured in the same manner as in Example 1,except that the vent member containing linear low-density polyethylene(LG Chem, Lucene™ SP311) having a comonomer with a carbon number of 6polymerized in the presence of a metallocene catalyst was insertedbetween the polypropylene resins.

Example 3

A secondary battery was manufactured in the same manner as in Example 1,except that the vent member containing linear low-density polyethylene(Dow, Elite™, 5401GT) having a comonomer with a carbon number of 8polymerized in the presence of a metallocene catalyst was insertedbetween polypropylene resins.

Comparative Example 1

After the upper pouch and the lower pouch on which polyethyleneterephthalate (poly(ethylene terephthalate))/aluminum foil/polypropyleneresin were laminated in order are disposed so that the polypropyleneresins face each other, an electrode assembly in which positiveelectrode/separator/negative electrode were stacked in order wasaccommodated therein.

After that, the polypropylene resins were thermally fused, therebymanufacturing a secondary battery.

Comparative Example 2

A secondary battery was manufactured in the same manner as in Example 1,except that the vent member containing linear low-density polyethylenehaving a comonomer with a carbon number of 4 polymerized in the presenceof a Ziegler-Natta catalyst was inserted between polypropylene resins.

Comparative Example 3

A secondary battery was manufactured in the same manner as in Example 1,except that the vent member containing high-density polyethylene(SABIC®, HDPE F04660) was inserted between the polypropylene resins.

Comparative Example 4

A secondary battery was manufactured in the same manner as in Example 1,except that the vent member containing linear low-density polyethylene(Dowlex™ 2645 G) having a comonomer with a carbon number of 6polymerized in the presence of a Ziegler-Natta catalyst was insertedbetween polypropylene resins.

Comparative Example 5

A secondary battery was manufactured in the same manner as in Example 1,except that the vent member containing linear low-density polyethylene(Dowlex™ 2045 G) having a comonomer with a carbon number of 8polymerized in the presence of a Ziegler-Natta catalyst was insertedbetween polypropylene resins.

Comparative Example 6

A secondary battery was manufactured in the same manner as in Example 1,except that the vent member containing linear low-density polyethylene(LG Chem, Lucene™ LF100) having a comonomer with a carbon number of 8polymerized in the presence of a metallocene catalyst was insertedbetween polypropylene resins.

Evaluation Example 1: Evaluation of Physical Properties of the ResinUsed in the Vent Member

The melting points, the comonomer contents, the weight-average molecularweights, the poly dispersity indexes, and the crystallizationtemperatures of the resins used in the vent members (also referredherein as ‘vent resin’) of Examples 1 to 3 and Comparative Example 2, 4to 6 and the sealant resin used in Comparative Example 1 were measured,as shown in Table 1 below.

(1) Measurement of Melting Point and Crystallization Temperature

The melting points and the crystallization temperatures of the sealantresin used in Comparative Example 1 and the vent resins used in the ventmembers of Examples 1 to 3 and Comparative Example 2, 4 to 6 weremeasured as follows.

The temperature of the sample was increased from 30° C. to 280° C. at10° C./min using a differential scanning calorimeter (DSC), maintainedat 280° C. for 10 minutes, cooled to 30° C. at 10° C./min, and thenmaintained at 30° C. for 10 minutes. Thereafter, after increasing thetemperature of the sample from 30° C. to 280° C. at 10° C./min, themelting point and the crystallization temperature were measured bymaintaining the temperature at 280° C. for 10 minutes.

(2) Measurement of Comonomer Content

The comonomer contents of the sealant resin used in Comparative Example1 and the vent resins used in the vent members of Examples 1 to 3 andComparative Example 2, 4 to 6 were measured using the H-NMR.

About 10 mg of the sample was completely dissolved in about 0.6 mL oftrichloroethylene solvent using a heater gun, then sampled in an NMRtube, and measured using the H-NMR.

(3) Measurement of Weight-Average Molecular Weight and Poly DispersityIndex

The weight-average molecular weights and the poly dispersity indexes ofthe sealant resin used in Comparative Example 1 and the vent resins usedin the vent members of Examples 1 to 3 and Comparative Example 2, 4 to 6were measured using gel permeation chromatography (GPC) under thefollowing conditions.

-   -   column: Tosoh, HLC-8321 GPC/HT    -   solvent: TCB (Trichlorobenzene)+0.04% BHT (after drying with        0.1% CaCl₂)    -   flow velocity: 1.0 ml/min    -   sample concentration: 1.5 mg/ml    -   dose: 300 μl    -   column temperature: 160° C.    -   Detector: RI detector    -   Standard: Polystyrene (calibrated with a third-order function)

TABLE 1 Com. Com. Com. Com. Com. Example 1 Example 2 Example 3 Ex. 1 Ex.2 Ex. 4 Ex. 5 Ex. 6 Melting 119 119 120 160 121 122 123 99 point (° C.)Content of 7.6 9.0 11.8 6 5.1 8.5 9.5 16.3 comonomer, based on entirevent resin content (weight %) Weight- 289,053 270,756 251,521 327,862272,870 282,456 267,347 205,603 average molecular weight (g/mol) Poly3.023 2.674 3.796 4.27 4.761 4.313 4.231 2.551 dispersity indexCrystallization 106 107 105 106 107 105 106 83 temperature (° C.)

Evaluation Example 2: Measurement of Sealing Strength According toTemperature

In the secondary batteries prepared in Examples 1 to 3 and ComparativeExamples 2 to 6, a tensile test was conducted at a speed of 5 mm/min,after cutting the part of the case in which the vent member was insertedinto a width of 15 mm and a length of 5 cm at the following temperatureand then gripping both ends thereof using a UTM jig in a state whereboth ends are spread to 180°. The sealing strength of the case at thistime is shown in Table 2 below.

In the secondary battery prepared in Comparative Example 1, a tensiletest was conducted at a speed of 5 mm/min, after cutting the case of thesealing portion into a width of 15 mm and a length of 5 cm at thefollowing temperature and then gripping both ends thereof using a UTMjig in a state where both ends are spread to 180°. The sealing strengthof the case at this time is shown in Table 2 below.

At this time, the maximum sealing strength means a maximum value whenthe case is broken, and the average sealing strength means an averagevalue when the case is stretched by 8 mm at 4.5 kgf/15 mm when themaximum sealing strength is 4.5 kgf/15 mm or more and an average valuewhen the case is stretched by 8 mm at the maximum sealing strength whenthe maximum sealing strength is less than 4.5 kgf/15 mm.

TABLE 2 Com. Ex. Example 1 Example 2 Example 3 Com. Ex. 1 2 Max. Ave.Max. Ave. Max. Ave. Max. Ave. Max. Ave. Sealing Room 11.1 9.4 14.6 9.513.8 9.0 13.9 9.7 0.5 — strength temp. (±0.6) (±0.2) (±3.0) (±0.1)(±1.1) (±0.01) (±0.5) (±0.1) (±0.2) (kgf/15 mm)  60° C. 7.2 5.9 13.3 7.610.0 7.0 12.9 7.2 0.1 — (±0.8) (±0.8) (±0.6) (±0.0) (±1.8) (±0.1) (±1.1)(±0.1) (±0.0) 100° C. 1.7 1.5 3.6 2.7 1.1 0.3 9.6 6.2 — — (±0.3) (±0.1)(±0.9) (±0.2) (±0.2) (±0.1) (±0.3) (±0.1) 120° C. 0.5 0.3 0.06 0.05 0.060.02 7.0 5.8 — — (±0.02) (±0.01) (±0.4) (±0.1) Com. Ex. 3 Com. Ex. 4Com. Ex. 5 Com. Ex. 6 Max. Ave. Max. Ave. Max. Ave. Max. Ave. SealingRoom 1.2 — 1.8 0.6 1.4 0.7 6.4 2.8 strength temp. (±0.3) (±0.5) (±0.1)(±0.3) (±0.3) (±0.4) (±0.5) (kgf/15 mm)  60° C. 0.6 — 0.5 0.2 0.7 0.42.4 0.8 (±0.1) (±0.1) (±0.02) (±0.3) (±0.2) (±0.5) (±0.2) 100° C. — — —— — 0.12 0.05 (±0.03) 120° C. — — — — — — —

As seen in Table 2, it was determined that in the secondary batteriesmanufactured in Examples 1 to 3, the part of the case in which the ventmember is inserted had a maximum sealing strength of 6.0 kgf/15 mm ormore and an average sealing strength of 4.5 kgf/15 mm or more at roomtemperature to 60° C., and had a maximum sealing strength of less than6.0 kgf/15 mm and an average sealing strength of less than 4.5 kgf/15 mmat 100° C. or above. Accordingly, the secondary battery having the ventmember manufactured in Examples 1 to 3 may ensure proper sealingstrength at room temperature to 60° C. at which the battery normallyoperates, and may discharge gas through the vent member having aweakened sealing strength when the battery is heated to high temperatureof 100° C. or above due to an abnormal phenomenon.

Meanwhile, it was determined that in the secondary battery manufacturedin Comparative Example 1, the case had a maximum sealing strength of 6.0kgf/15 mm or more and an average sealing strength of 4.5 kgf/15 mm ormore at room temperature to 60° C., but also had a maximum sealingstrength of 6.0 kgf/15 mm or more and an average sealing strength of 4.5kgf/15 mm or more at 100° C. or above. Accordingly, the secondarybattery manufactured in Comparative Example 1 may secure proper sealingstrength at room temperature to 60° C. at which the battery normallyoperates. However, when the battery is heated to high temperature of100° C. or above due to an abnormal phenomenon, gas is discharged inunspecified directions, which would cause ignition of the battery.

In the secondary batteries manufactured in Comparative Examples 2 to 6,the part of the case in which the vent member is inserted had a maximumsealing strength of less than 6.0 kgf/15 mm and an average sealingstrength of less than 4.5 kgf/15 mm at room temperature to 60° C. At atemperature of 100° C. or above, the sealing strength was too low to bemeasured. From this, it was determined that the secondary batteriesmanufactured in Comparative Examples 2 to 6 cannot secure proper sealingstrength strength at room temperature to 60° C. at which the batterynormally operates.

What is claimed is:
 1. A secondary battery, comprising: an electrodeassembly; an electrode lead attached to the electrode assembly; a caseconfigured to receive the electrode assembly therein; a lead filmconfigured to surround a part of an outer surface of the electrode lead,the lead film being interposed between the electrode lead and the case;a vent region formed in at least a part of the case; and a vent memberinserted into the vent region, wherein the vent member contains linearlow-density polyethylene having a poly dispersity index (PDI) of 4 orless, wherein the vent member has a maximum sealing strength of lessthan 6 kgf/15 mm at 100° C. or above and a maximum sealing strength of 6kgf/15 mm or more at room temperature to 60° C.
 2. The secondary batteryaccording to claim 1, wherein the vent member has an average sealingstrength of less than 4.5 kgf/15 mm at 100° C. or above.
 3. Thesecondary battery according to claim 1, wherein the vent member has anaverage sealing strength of 4.5 kgf/15 mm or more at room temperature to60° C.
 4. The secondary battery according to claim 1, wherein the caseincludes a sealing portion formed to seal the electrode assembly, thesealing portion contains a sealant resin, and the linear low-densitypolyethylene has a lower melting point than the sealant resin.
 5. Thesecondary battery according to claim 1, wherein the vent member melts at100° C. to 120° C. to vent gases.
 6. The secondary battery according toclaim 5, wherein the vent member is vented at a pressure of 1.5 atm ormore.
 7. The secondary battery according to claim 1, wherein the linearlow-density polyethylene is made by polymerizing in the presence of ametallocene catalyst.
 8. The secondary battery according to claim 4,wherein a difference between a crystallization temperature of thesealant resin and a crystallization temperature of linear low-densitypolyethylene is 10° C. or less.
 9. The secondary battery according toclaim 8, wherein the linear low-density polyethylene has acrystallization temperature of 90° C. to 115° C.
 10. The secondarybattery according to claim 1, wherein the linear low-densitypolyethylene has a melting point of 100° C. to 130° C.
 11. The secondarybattery according to claim 1, wherein the linear low-densitypolyethylene has a weight-average molecular weight of 100,000 g/mol to400,000 g/mol.
 12. The secondary battery according to claim 4, whereinthe vent region is located in the sealing portion.
 13. The secondarybattery according to claim 12, wherein the vent region is located in asealing portion at a corner of the case.
 14. The secondary batteryaccording to claim 1, wherein the secondary battery is a pouch-typesecondary battery.
 15. The secondary battery according to claim 1,wherein the vent member has a maximum sealing strength of less than 6kgf/15 mm at 100° C. to 120° C.
 16. The secondary battery according toclaim 1, wherein the vent member has an average sealing strength of lessthan 4.5 kgf/15 mm at 100° C. to 120° C.
 17. The secondary batteryaccording to claim 1, wherein the linear low-density polyethylene has apoly dispersity index (PDI) of from 1 to
 4. 18. The secondary batteryaccording to claim 1, wherein the vent member has a maximum sealingstrength of less than 3 kgf/15 mm at 120° C. or more.
 19. The secondarybattery according to claim 1, wherein the vent member has an averagesealing strength of less than 2 kgf/15 mm at 120° C. or more.